(SERVER-104) Added docs for ext. SSL termination
(SERVER-104) Updated spelling/grammar and wording
(SERVER-104) Updated link
(SERVER-104) Clarification
(SERVER-104) Further clarification
Merge pull request #242 from dankreek/SERVER-104/document-certs-in-x-headers

(SERVER-104) Added docs for external SSL termination
(SERVER-103) External CA documentation

This commit includes a new document which covers the use of an external
CA with Puppet Server.  This commit also adds a link to the new document
from a couple of existing documents.
(SERVER-103) Added blank lines between setting names and fixed link

This commit adds some blank lines between settings in the
`webserver.conf` example and fixed the link for the `X-Client` headers
to point to the new doc that SERVER-104's PR will introduce.